Heterogeneity of platelets would be further examined with respect to platelet membrane proteins, glycoproteins; platelet microtubules, and their possible relationship to platelet aging. With the use of a quantitative fluorescent antibody technique, platelet antibody bound to platelets would be examined. Bound anti-platelet antibody can be eluted and reabsorbed to other platelets. Techniques would be designed to bind this eluted anti-platelet antibody to platelet membrane proteins. With this approach, platelet 'autoimmune' antigens might be determined. The pathophysiology of autoimmune thrombocytopenic purpura would be further examined with respect to antibody directed against other tissues; particularly red blood cells (since red blood cell fragments have been detected in these patients) and granulocytes. The same technique for the detection of bound antiplatelet antibody would be adapted to the detection of bound anti-granulocyte antibodies.